1. Field of the Invention
The present invention relates to a memory device and a method of operating the same, and more particularly, to a memory device using an abrupt metal-insulator transition (MIT) and a method of operating the same.
2. Description of the Related Art
An example of a memory device is a phase change memory device that uses a structural phase change between a crystalline phase and an amorphous phase. This phase change memory device requires a high melting temperature of a phase change material and a large amount of time for crystallization, and is thus unreliable in a repetitive switching operation. The reason for this is that the phase change memory device uses a structural phase change of a phase change material.
Another example of a memory device is a resistance change memory device that uses a resistance change accompanied with the structural phase change of a material. This resistance change memory device is disclosed in U.S. Pat. No. 5,761,115, U.S. Pat. No. 5,896,312, U.S. Pat. No. 5,914,893, U.S. Pat. No. 6,084,796, U.S. Pat. No. 6,653,193, and Paper of S. Seo et al. [Appl. Phys. Lett. 85, p 5655, 2004]. According to these documents, the resistance change memory device uses a dendrite conductor (or a fast ion conductor) contained in a material with a variable resistance (hereinafter referred to as a resistance change material). That is, when a voltage is applied to the resistance change material, the dendrite conductor grows or reduces in size, leading to the resistance change of the resistance change material. Specifically, when a positive voltage is applied to the resistance change material, the dendrite conductor grows to form a conducting path between electrodes causing the resistance change material to change into a low-resistance state. On the other hand, when a negative voltage is applied to the resistance change material, the dendrite conductor reduces in size to reduce the size of the conducting path causing the resistance change material to change into a high-resistance state.
However, the resistance change memory device undergoes a structural phase change of the resistance change material. That is, the resistance change material includes the dendrite conductor and is thus a non-uniform material with at least two phases. Also, when the dendrite conductor is not created or is low in concentration, the resistance change memory device cannot meet memory characteristics. Furthermore, since the resistance change memory device generates heat in the high-resistance state, the resistance change memory device may lose memory characteristics after long usage.
In summary, since the phase change memory device and the resistance change memory device undergo a structural phase change, the phase change memory device and the resistance change memory device are unsuitable as a high-speed switching device. Therefore, an improved memory device that undergoes no structural phase change, maintains a uniform thin film, and can perform a high-speed switching operation which is required.